Method for feeding electrical power into an electrical supply network

ABSTRACT

The invention relates to a method for feeding electrical power into an electrical supply network by means of at least a first and a second wind farm. A first electrical wind farm output is provided by the first wind farm to be fed into the electrical supply network and a second electrical wind farm output is provided by the second wind farm to be fed into the electrical supply network, and a total power output is generated from at least the first and second wind farm output and fed into the electrical supply network, wherein a central control unit for controlling the total power output that is fed in controls the provision of at least the first and second wind farm output.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2014/059099, filed May 5, 2014, which claims priority to GermanApplication No. 10 2013 208 474.9, filed May 8, 2013, the entirecontents of both of which are incorporated herein by reference in theirentirety for all purposes.

The present invention relates to a method for feeding electrical powerinto an electrical supply network. In addition, the present inventionrelates to a wind farm arrangement for feeding electrical power into anelectrical supply network.

It is generally known that wind power installations can generate andfeed electrical power into an electrical supply network. A correspondingwind power installation is schematically shown in FIG. 1. Increasingly,instead of operating a single installation, a plurality of wind powerinstallations is installed in a wind farm, which is capable of feeding acorrespondingly large amount of power into the supply network. Such awind farm is shown schematically in FIG. 2 and is characterized inparticular by a point of common coupling, by means of which all windpower installations of the wind farm feed into the electrical supplynetwork.

Such wind farms are not only able to feed a large quantity of power intothe electrical supply network, but also have a correspondingly largecontrol potential for the stabilization of the electrical supplynetwork. In this regard, for example, the US patent application U.S.Pat. No. 7,638,893 suggests that the operator of the electrical supplynetwork, for example, can provide the wind farm with a power parameterin order to reduce the wind farm output to be fed in, in order to havean additional control option for the supply network thereof.

Depending on the size of the wind farm, such control options may be weakand in addition may be difficult to manage due to the fact that windpower installations and wind farms are decentralized production units,because they are distributed over a comparatively large area of a regionin which the respective electrical supply network is operated.

In addition, in many countries such as Germany, efforts are being madeto replace conventional large-scale power plants, in particular nuclearpower plants, with renewable energy generators such as wind turbines.However, this raises the problem that with the shutting down and removalof a large-scale power plant from the grid, the grid stabilizationeffect of that plant is also lost. The remaining or newly added powergenerating units are thus needed in order to at least take into accountthis change of stability.

The object of the present invention is thus to address at least one ofthe aforementioned problems and, in particular, to provide a solutionfor further increasing or improving the support of an electrical supplynetwork by means of wind farms in order to be able to create as stable asupply network as possible. At least one alternative solution should beproposed.

What is proposed in accordance with the invention is therefore a methodaccording to some of the claims. Accordingly, at least two wind farmsfor feeding electrical power into an electrical supply network are takenas a basis. The first and second wind farms hereby described arerepresentative for two or more wind farms. The teaching is accordinglyapplicable to a third and additional wind farm. The third or,respectively, each additional wind farm accordingly has the samemechanisms, connections, control options and behavior described for thefirst and second wind farm.

In this way, at least a first electrical wind farm output is provided bythe first wind farm and at least a second electrical wind farm output isprovided by the second wind farm and both wind farm outputs are finallyto be fed into the supply network. A total power output is generatedfrom these at least two wind farm outputs, namely the total of these twowind farm outputs and, in the case that more than two wind farms areused, the respective wind farm output is added accordingly to this totalpower output. This total power output is now fed into the electricalsupply network.

In addition, a central control unit is proposed, which controls theprovision of the first and second wind farm output in order to controlthe total power output that is fed in. If the total power output isgenerated by additional wind farm outputs, thus a third and, ifapplicable, even an additional wind farm output, it is providedaccordingly that this central control unit also controls this wind farmoutput in order to thereby control the total power output, which is tobe fed into the electrical supply network.

Thus a central control of a very large quantity of power is therebyproposed, namely of a power that represents the power of at least twowind farms. A control potential can hereby be increased because inessence, from the perspective of the electrical supply network, insteadof two or more smaller amounts of power, only one large amount of poweris fed into the grid and may also be controlled according to therespective desired requirements.

The proposed method thus reduces the decentralized control that ischaracteristic of wind power installations, as well as of wind farms.The more wind farms that are jointly controlled in this manner, theindividual wind farm outputs thus being fed in together as a total poweroutput and this feeding in being coordinated by the central controlunit, the more it will be possible to convert what has previously been adecentralized control into a centralized control.

In particular it is possible to avoid each individual wind farm havingits own control, wherein the controls of a plurality of wind farms aredifficult to coordinate with one another and, in the worst casescenario, even work against one another.

The risk that two wind farms that feed into the same supply network willwork against one another may also arise when both wind farms haveimplemented the same control to support the supply network. For example,even small measurement inaccuracies may lead to different supportbehavior or, respectively, control behavior of the two wind farms namedin the example. Even minimal time shifts between the two wind farms maybe problematic. With even the smallest difference, there may be a riskthat the one wind farm already interjects control into the grid beforethe second wind farm is able to do so.

For example this may mean that such a controlling or, in particular,supporting effect of the first wind farm is already so successful thatthe second wind farm does not even enter a range in which it can exert acontrolling effect. The result in this example is that the controlpotential of the second wind farm remains unused. In extreme situationsthe result may be that the second wind farm attempts to cancel thecontrol success of the first wind farm and, as a result, both wind farmsactually work against one another. All of this is avoided by means ofthe proposed method.

Preferably each of these wind farms comprises a wind farm control unitfor controlling the respective wind farm. The central control unit isconnected to this wind farm control unit and the central control unitcontrols the provision of the first and second wind farm output and,where applicable, additional wind farm outputs in turn, by means of therespective wind farm control unit of the respective wind farm. Inparticular, the central control unit provides each of these wind farmcontrol units with appropriate control commands. In addition, therespective wind farm control units can return needed information to thecentral control unit. The concrete control of each wind farm can therebybe performed by the individual wind farm control units and the centralcontrol unit can control the coordination of the appropriate wind farmsamong one another by means of default values, which each wind farm thenimplements accordingly with the help of the wind power installationsthereof.

To this end, the central control unit preferably records statusvariables from the supply network, which are needed for thiscoordination. The central control unit may also record status variablessuch as frequency, phase and voltage amplitude for the wind farm,however, and provide these for the needs thereof.

In addition or alternatively, the central control unit records valuesfor the total power output fed in. The central control unit can thuscontrol the total power output that is fed in from the wind farmscontrolled by said central control unit, such wind farms being referredto as combined wind farms for the sake of simplicity, and can make thenecessary controls as appropriate as a function thereof. In addition oralternatively, it is proposed that the central control unit be able torecord external default values, and in particular be able to receivesuch values from the operator of the supply network for example. Thus adefault value may be received at a central location and taken intoconsideration in order to coordinate the combined wind farms basedthereon. For example, a maximum quantity of power to be fed in may bespecified and compared to the total power output that is fed in. Thecentral control may influence the control of the wind farm as a functionof this comparison and, if applicable, may send corresponding controlsignals to a wind farm or a plurality of wind farms in order toinfluence the respective wind farm output. The total power output can beinfluenced thereby and adjusted to the desired value.

According to one embodiment, it is proposed that the method becharacterized in that at least the first and second wind farm feed thefed-in power that they are to provide into an intermediate network,wherein

-   -   in each case, the intermediate network is connected to the        respective wind farm by means of a transformer to step up an        electrical voltage in the wind farm to a higher electrical        voltage in the intermediate network and/or    -   the intermediate network is connected to the electrical supply        network by means of a transformer to step up an electrical        voltage in the intermediate network to a higher electrical        voltage in the supply network.

Thus an intermediate network is proposed, which connects the two windfarms or additional wind farms controlled by means of the methodrespectively, in essence in order to collect the wind farm outputs onthe intermediate network and to also form the total power output here inorder to feed that output from the intermediate network to theelectrical supply network. A step-up of the wind farm voltages, thus ofthe voltage of the respective wind farm, may be performed for each windfarm by a transformer. Thus the voltage of each wind farm is stepped upbefore it is provided to the intermediate network. In addition oralternatively, a transformer is provided in order to step up the voltagein the intermediate network to the voltage in the supply network. It mayalso be provided that the respective wind farm voltage is stepped up toa higher voltage in the intermediate network and, in addition, that thishigher voltage of the intermediate network is further stepped up to aneven higher voltage in the supply network. The intermediate networkpreferably has a medium voltage, specifically in the range of 1 to 50kV, and the electrical supply network has a high voltage, specificallyhaving a voltage value of approximately 110 kV.

The central control unit preferably records the total power output fedinto the supply network in the region or, respectively, at a connectionpoint at which power is fed from the intermediate network into thesupply network. This is advantageously implemented in the region of thetransformer between the intermediate network and the supply network orthere before the transformer.

A further embodiment of the invention proposes that the central controlunit controls the feed into the electrical supply network as a functionof at least one status variable in the supply network, controls the feedas a function of a grid sensitivity of the supply network with referenceto the infeed node, and, in addition or alternatively, that it controlsthe feed as a function of a short-circuit ratio.

In particular, the grid frequency f, a change in the grid frequency∂f/∂t, and the line voltage U are used as status variables. Inparticular, the central control unit ensures that a total power outputis fed into the supply network pursuant to a parameter, which may havebeen defined by the operator of the supply network. Furthermore, namelyin addition, a control of the feeding in may be provided as a functionof a status variable making it possible to react dynamically to eventsin the supply network. For example, it may be provided that the totalpower output that is fed in is reduced when there is an increase in thegrid frequency f above a threshold value, which lies above the nominalvalue. Thus it is proposed that such a dynamic adjustment control becentrally provided for dynamic stabilization or, respectively, thesupport of the supply network, namely by means of the central controlunit. This may be performed in such a way that the central control unitrelays appropriate control values or control commands to the wind farmcontrol units. The wind farm control units, in turn, can relay convertedvalues to the individual wind power installations in the appropriatewind farm.

As a result, these two wind farms function as a unit to affect thesupply network, which thereby has a very high control potential, namelythe power of at least two wind farms. It is thereby possible to avoidthe individual wind farms thus connected or even individual wind powerinstallations in the wind farm from working against one another. Inaddition, this method also simplifies the control for the operator ofthe supply network, because to this end, said operator only needs totransmit a target value or other desired value to a central controlunit. A parameter for a unit having a very large available line ishereby also actuated.

The specified wind farm output and the specified total power outputessentially refer to active power. Nonetheless, it is preferablyproposed as an alternative that the method features described for thispower, thus the active power, in turn be used for a reactive powercontrol. The central control unit can hereby specify a desired reactivepower feed for the individual wind farm, in order to thereby be able torealize a desired total reactive power feed, thus the feed in of a totalreactive power output. Such a reactive power feed is used in particularas a function of the voltage U of the supply network. According to oneembodiment, it is proposed here that the control unit carry out anincreasing reactive power feed with a drop in line voltage when the linevoltage falls below a threshold value below the nominal voltage, to nameonly one example.

There is also a large control potential available for such a reactivepower control by means of the central control unit because the controlpotential of all of the combined wind farms, thus at least the two windfarms specified in the example together, is available to the centralcontrol unit. Insofar as such a grid state, for example the line voltagespecified in the example, is at its nominal value or at least deviatesonly within a tolerance range thereof, such a reactive power control canprovide that no reactive power is fed in.

An additional variable for improving grid support is the observation ofthe grid sensitivity. Such grid sensitivity can provide information onthe current strength or, respectively, stability of the supply network,in particular with reference to the feed point for the total poweroutput. The grid sensitivity may thereby intervene directly in suchpower control, however it is preferably suggested that a controlalgorithm be selected, adapted and/or modified as a function of the gridsensitivity, it being possible however for said control algorithm tohave other initial parameters. The quality and dynamics of the gridcontrol in particular can hereby be adapted to the current requirementsof the supply network, which is referred to simply as the grid.

Grid sensitivity here means the grid's reaction, in particular inrelation to the point of common coupling, to a change in a parameteraffecting the grid. Grid sensitivity can be defined as the difference ofa grid reaction in relation to a difference of a grid influenceparameter. What is used here, in particular, is a definition in relationto the fed-in active power and line voltage level. Put in simplifiedterms, the following formula can be defined, for example, for the gridsensitivity NS:

${NS} = \frac{\Delta \; U}{\Delta \; P}$

Here, ΔP describes the change in fed-in active power, namely the fed-intotal output, and ΔU describes the resulting change in the line voltageU. These differences are created over a very brief period of time, inparticular in the area of one second or less, and advantageously,instead of using this descriptive formula, a partial derivation of theline voltage U, namely in particular the effective value thereof, can bealso created based on the fed-in wind farm output P according to thedifference of the voltage in relation to the difference of the power.Another possible grid reaction could be the change in grid frequency f.Another way of considering grid sensitivity would be to apply thefollowing formula:

${NS} = \frac{\Delta \; f}{\Delta \; P}$

It is preferably further proposed that a short circuit current ratio beconsidered and that the infeed be controlled by means of the centralcontrol unit as a function of said short circuit current ratio. For thatpurpose, it is also proposed in particular that a control algorithm beselected, adjusted and/or modified as a function of the short circuitcurrent ratio.

Short circuit ratio (also referred to as SCR) means the ratio of shortcircuit power to connected load. Short circuit power is the power thatthe respective supply network can provide at the considered point ofcommon coupling to which the wind power installation, the wind farm or,respectively, the proposed combined wind farms is/are connected, ifthere is a short circuit at the point of common coupling. The connectedload is the connected load of the connected wind power installation, ofthe connected wind farm or, respectively, the proposed combined windfarms, and thus—in particular—the nominal power of the generator that isto be connected or, respectively, the sum of all nominal powers of thegenerators of the wind farm or farms. The short circuit ratio is thus acriterion for the strength of the electrical supply network in relationto such considered point of common coupling. A strong electrical supplynetwork relating to said point of common coupling has mostly a largeshort circuit ratio of, for example, SCR=10 or greater.

It has been recognized that the short circuit ratio can also provideinformation on the behavior of the respective supply network at thepoint of common coupling. The short circuit ratio may also vary.

When installing a combined wind farm for the first time, it isadvantageous to consider the short circuit ratio and to adapt the activepower control and the reactive power control thereto. It is preferablyfurther proposed to record the short circuit ratio on a regular basiseven after the installation and commissioning of the combined windfarms. The short circuit power can be recorded, for example, based oninformation on the grid's topology using simulation. The connected loadcan be determined simply by having knowledge of the wind powerinstallations installed in the combined wind farms and/or by measuringthe unrestricted, total power fed in at nominal wind.

A connected load for the proposed calculation and taking into account ofthe short-circuit ratio is preferably defined and calculated as the sumof the nominal power of all respective, currently available wind powerinstallations. In this sense, the connected load would already changewere one wind power installation to fail, at least on a temporary basis.The short circuit current ratio would thereby also change and this couldtrigger a change in the active power control and/or the reactive powercontrol.

One embodiment proposes that the central control unit for the feed intothe electrical supply network

-   -   control the amount of active power to be fed in,    -   control the amount of reactive power to be fed in, and/or    -   control the consumption of electrical power in a power        consumption device, in particular in a loss resistance device.

The central control unit can thus control the amount of active power tobe fed in and, in addition or alternatively, can control the amount ofreactive power to be fed in, as described above in conjunction withvarious embodiments. In addition, the method may stipulate that theconsumption of electrical power be controlled in a power consumptiondevice. In particular, the consumption of electrical power in a lossresistance device is considered here. To this end, such a powerconsumption device may be provided in one, a plurality, or allcoordinated wind farms. Such a power consumption device is preferablydisposed outside of the wind farms however, which may be referred tosimply as farms, and can be directly controlled by the central controlunit.

In particular when an intermediate network is provided, the wind farmsare coupled to this intermediate network and at least one powerconsumption device is coupled to this intermediate network. Theselective consumption of electrical power may be provided in order totemporarily consume excess power from one, a plurality of, or allcoordinated wind farms when, for example, the power to be fed in must beabruptly reduced and the wind power installations of the wind farmscannot reduce the withdrawal of power from the wind quickly enough.

In addition or alternatively, it is proposed that such a powerconsumption device also specifically create the possibility of removingpower from the supply network in the event that an excess should prevailthere and the power stations that are feeding this excess in cannotreduce their infeed power quickly enough.

If this at least one power consumption device is directly connected tothe intermediate network, it may nevertheless be available to the windfarms. In addition, it can absorb excess power from the supply networkwithout influencing the wind farms.

A device is suggested as a power consumption device, which preferablyutilizes the power that is to be consumed as usefully as possible. Thedevice may perform work or, in particular, may provide interim storagefor the excess power and in addition, if applicable, may convert saidenergy into another form of energy for better storage. This powerconsumption device is preferably also a bi-directional power converterand/or an energy accumulator.

A preferred embodiment proposes that

-   -   the central control unit record current status variables in the        electrical supply network, in particular frequency and voltage        amplitude, and that the unit control at least the provision of        the first and second wind farm output as a function thereof        and/or    -   each wind farm control unit provides information concerning at        least one status variable for the respective wind farm and the        information contains at least        -   the currently available power,        -   the power expected to be available within a predetermined            forecast period and        -   changes expected in the available power.

The central control unit is thus also used as a measuring unit, inparticular in order to record the frequency amplitude and voltageamplitude of the voltage in the supply network. These variables can beused to control the provision of the first and second and, ifapplicable, additional wind farm output as a function thereof. Thechange in voltage ∂f/∂t described in conjunction with an embodiment canalso be determined from this detected frequency of the voltage of thesupply network. This information may also be provided for use by thecoordinated wind farms, in particular the wind farm control unitsthereof.

In addition or alternatively, each wind farm control unit provides thecentral control unit with information regarding the current state of thewind farm, thus with status variables for the respective wind farm, inparticular namely the currently available power, the power expected tobe available shortly, and expected changes in the available power. Thecentral control unit can evaluate this information concerning the poweraccordingly and, in light of such information, can merge all coordinatedwind farms accordingly. Information regarding the expected power andexpected changes in the power can be determined in the respective windfarm, in particular by means of wind forecasts. In one case, this may bea meteorological evaluation. In other cases, especially when the windfarm is spread out over a comparatively large area, the increase ordecrease in the wind may be detected at some windward wind powerinstallations. The wind farm, which controls and monitors all of thesewind power installations, can derive a forecast therefrom for the windpower installations located behind those that are windward and a powerforecast can be derived therefrom and provided to the central controlunit in a timely manner. If applicable, the central control unit canrelay the appropriate information on to the operator of the supplynetwork based on that information or other information.

The central control unit is preferably prepared to function as a phaseshifter. The central control unit hereby takes power from the supplynetwork and feeds that power into the electrical supply network as aninfeed current with a phase angle, which is modified or, respectively,adjusted as desired. Such a central control unit can perform thisfunction even when the wind farms are providing no power, for examplewhen there is a dead calm. However the central control unit ispreferably prepared to perform such a phase shift operation concurrentto the infeed of the total power output. The possibility for gridsupport can be increased by this combined operation by the centralcontrol unit.

Power is preferably fed into the grid in such a way that disturbances inthe supply network are entirely or partially compensated for. To thisend, the central control unit detects disturbances, for example such asharmonics, and feeds power in as compensation. In this case, currentthat is not ideal, which is to say non-sinusoidal current, isspecifically fed in, which current deviates from the ideal sinusoidalcharacteristic in such a way that these deviations, which themselvesessentially represent disturbances, compensate as much as possible for,or at least reduce the disturbances in the grid.

In addition, a wind farm arrangement pursuant to some of the claims isproposed. This arrangement is prepared for feeding electrical power intoan electrical supply network and comprises at least a first and a secondwind farm, each comprising a plurality of wind power installations.Furthermore, the arrangement comprises an intermediate electrical gridthat is connected to the wind farms to pass on electrical wind farmoutput, which is provided by the respective wind farm. The wind farmsare thus prepared to feed into this intermediate network. Further, thiswind farm arrangement comprises a central control unit, which controlsthe infeed of a total power output. This total power output merges thewind farm outputs that were fed into the intermediate network or thatwere provided by means of the intermediate network, and the centralcontrol unit is prepared to control these provided wind farm outputs. Inparticular, the central control unit is linked with the individual windfarms, in particular with a wind farm control unit for each park, bymeans of a data connection. This connection may be wired or wireless.

In particular, it is provided that the wind farm arrangement be designedto carry out at least one process in accordance with one of theembodiments described above.

To this end, appropriate control functions, in particular controlprograms, must be implemented in the central control unit andcorresponding communication channels are needed between the centralcontrol unit and the wind farm control units. Depending on theembodiment of the method to be used, additional elements, in particularsensors and/or a frequency inverter and/or a phase shifting device, maybe provided.

In addition, it is proposed that the intermediate network be connectedto each of the wind farms by means of a transformer, in order to step upan electrical voltage in the wind farm to a higher electrical voltage inthe intermediate network, and in addition or alternatively, that it beprovided that the intermediate network be connected to the electricalsupply network by means of a transformer, in order to step up anelectrical voltage in the intermediate network to a higher electricalvoltage in the supply network. Thus it is proposed that a wind powerinstallation arrangement can perform such a step up in the voltagebetween the wind farm and the intermediate network and/or between theintermediate network and the supply network, as described in conjunctionwith some embodiments of the proposed method.

It is preferably proposed both for the wind farm arrangement and for themethod to be used for the infeed that a desired voltage target value beprovided to the central control unit as a reference value for thevoltage of the supply network externally, in particular by an operatorof the supply network. In addition or alternatively, it is proposed thata maximum power value and/or a desired power value be set for thecentral control unit. In addition, it is also proposed as an embodimentthat a desired reserve power be sent to the central control unit as adefault value. Such a reserve power is the power at which the totalpower output that is fed in lies below the current possible total poweroutput that may be fed in. To this end, a percentage or an absolutespecification for the reserve power, for example, can be passed to thecentral control unit.

The central control unit preferably transmits to the wind farm controlunits a value for a reactive power that is to be fed in as a reactivepower target value, an upper limit for the active power as a power valuethat the respective wind farm must currently not exceed, and in additionor alternatively, it is proposed that the central control unit transmita power reserve, which is also referred to as a reserve capacity, to thewind farm control unit as a target value. The individual wind farms andthus, overall, the total power output can thus be operated below acurrent possible power value. This reserve capacity is thus available asa potential positive operating reserve, thus as power that can be fedin, in addition, as needed.

According to an additional embodiment, it is proposed that each windfarm control unit and/or each wind power installation of the wind farmcan each independently provide a grid-state dependent control, inparticular a frequency-dependent power control, namely if the centralcontrol unit or, respectively, a corresponding wind farm control unitfails. Insofar as in this case only information-processing elements havefailed, however the physical connection to the supply network continuesto be available, infeed can be continued and a dynamic grid support or,respectively, grid stabilization may even be performed.

Thus many embodiments both of a method and for a wind farm arrangementhave been described based on the present invention, which embodimentsprovide, inter alia, the option that a plurality of wind farms can feedpower into the electrical supply network in a coordinated manner and canthereby function in the manner of a large-scale power plant in terms ofgrid behavior. Purely as a precaution, it should be noted that a centralcontrol can develop a beneficial effect, namely such as described above,however, when a plurality of feed points for the infeed of power arephysically provided in the electrical supply network, however as long asthe infeed is centrally, and, in particular, consistently controlled.Preferably, however, the entire total power output is fed into a pointof common coupling in the electrical supply network.

The invention is now described in more detail below using embodiments asexamples with reference to the accompanying figures.

FIG. 1 schematically shows a wind power installation.

FIG. 2 schematically shows a wind farm.

FIG. 3 schematically shows a wind farm arrangement.

FIG. 1 shows a wind power installation 100 having a tower 102 and anacelle 104. A rotor 106 with three rotor blades 108 and a spinner 110is arranged on the nacelle 104. When in operation, the rotor 106 isbrought to a rotating movement by the wind and thereby drives agenerator in the nacelle 104.

FIG. 2 shows a wind farm 112 with, for example, three wind powerinstallations 100, which may be the same or differ. The three wind powerinstallations 100 are thus representative of a basically random numberof wind power installations of a wind farm 112. The wind powerinstallations 100 provide their power, in particular the generatedelectricity, via an electrical wind farm grid 114. The currents or,respectively, powers generated by the individual wind powerinstallations 100 are added up. Most often, a transformer 116 will beprovided, which transports the voltage at the wind farm to then feed itinto the supply network 120 at the feeding point 118, which is alsogenerally referred to as a PCC. FIG. 2 is merely a simplifiedillustration of a wind farm 112, which does not show, for example, acontrol, although a control exists, of course. Also, the wind farm grid114 may be designed differently, including, for example, a transformerat the output of each wind power installation 100, to mention just oneother embodiment.

FIG. 3 shows a wind farm arrangement 1 having two wind farms 112 by wayof example, which may also have a different design, a central controlunit 2 and a power consumption device 4. The wind farm arrangement 1 isthereby connected to the electrical supply network 120 at the point ofcommon coupling 6, which supply network is merely indicated here.

FIG. 3 shows two wind farms 112 as an example, which have a plurality ofwind power installations 100, for the wind farm arrangement 1. The windpower installations 100 of each wind farm 112 each generate a wind farmoutput P_(P1) or, respectively, P_(P2) that is provided to anintermediate network 10 by means of a wind farm transformer 8 and whichare available to feed into the supply network 120 as a total poweroutput P_(S). Assuming initially that the power consumption device 4 isnot active, the total power output P_(S) is the total of the wind farmoutput P_(P1) and P_(P2) and thus satisfies the equationP_(S)=P_(P1)+P_(P2).

This total power output P_(S) is fed into the supply network 120accordingly at the grid connection point 6 by means of the feedtransformer 12.

Here, the central control unit is disposed in the region of the gridconnection point 6 upstream from the feed transformer 12. There, thecentral control unit can also record the power P_(S) that is fed in.

The central control unit 2 is thereby connected to a control unit 16 ofthe operator of the electrical supply network 120 by means of a powersupply company (PSC) data connection 14. The central control unit 2 canreceive data from the control unit 16 of the grid operator, for examplesuch as a value for the total power output P_(S) to be fed in, by meansof the PSC data connection 14, and can transfer data, for example suchas information concerning the currently available total power outputP_(S). In general, all of the data connections in FIG. 3 are illustratedas a dashed line.

The central control unit is connected to each wind farm control unit 20of the respective wind farm 112 by means of a wind farm controlconnection 18. The central control unit 2 can transmit data to therespective wind farm control unit 20 by means of these wind farm controlconnections 18, in particular target values for the wind farm output,P_(P1) or, respectively, P_(P2), that is to be fed in. It should benoted that the reference signs of both wind farms 112, with theexception of the wind farm output P_(P1) or, respectively, P_(P2), areidentical in order to clarify the analogies between the two wind farms.The individual elements such as the wind farm transformer 8 may beconfigured differently, however.

Other types of communication may be undertaken between the centralcontrol unit 2 and the respective wind farm control unit 20 by means ofthe wind farm control connection 18. In so doing, for example, the windfarm control unit 20 may provide the central control unit 2 withinformation concerning the currently available wind farm output.

Each wind farm control unit 20 is, in turn, connected within its ownwind farm 112 by means of a wind farm data network 22 for the exchangeof data with the respective wind power installations 100. The wind farmcontrol unit 20 may thereby relay the respective default values that ithas received from the central control unit 2 to the wind powerinstallations 100 in order to control the wind farm 112. In addition,the wind farm control unit 20 may receive information regarding thisfrom the wind power installations 100 and, if applicable, may evaluatethis information and if desired may relay that information to thecentral control unit 2.

Thus, the central control unit 2 can control the infeed of the totalpower output P_(S) in that said central control unit controls theindividual wind farm outputs P_(P1) and P_(P2) by means of controllingthe wind farm control units 20.

In addition, the power consumption device 4 is connected to the powerconsumption device 4 by means of a consumption control connection 24.The central control unit can in particular exert control hereby whenexcess power is to be consumed by means of the power consumption device4. This may be excess power from the wind farms 112, or also excesspower from the supply network 120. To this end, the power consumptiondevice 4 is connected to the intermediate network 10 by means of thepower consumption connection 26. The power consumption connection 26 mayalso form a part of the intermediate network 10.

The power consumption device 4 is labeled here with different symbolsfor different embodiments. A chopper circuit 28 thereby symbolizes apure power consumption unit, which converts electrical power or,respectively, electrical energy into heat, which can be done usingappropriately controlled thermal resistances.

In addition, a conversion means 30 is symbolized, which can convert theelectrical power into another medium such as a gas, for example. Thisconversion means 30 is preferably designed in such a way that the energyfrom this other medium, for example gas as mentioned in this example,can also be converted back into electrical energy, at least in part. Inthis case, the result of such a re-conversion would be that the powerconsumption device 4 could also provide power to the intermediatenetwork 10 and to this extent, in addition to the wind farm outputsP_(P1) and P_(P2), the total power output P_(S) would also have areturned power consumption.

Finally, an accumulator in the form of a battery storage 32 is alsosymbolized in the power consumption device 4, which is able to directlystore electrical energy.

FIG. 3 thus illustrates a wind farm arrangement, which is prepared toimplement a method according to the invention for the infeed ofelectrical power pursuant to at least one of the described embodiments.

1. A method for feeding electrical power into an electrical supplynetwork by means of at least a first and a second wind farm, comprisingthe steps: Provision of a first electrical wind farm output by the firstwind farm for feeding into the electrical supply network, Provision of asecond electrical wind farm output by the second wind farm for feedinginto the electrical supply network, Generation of a total power outputfrom at least the first and second wind farm output and feeding in ofthe total power output into the electrical supply network, wherein acentral control unit for controlling the total power fed in controls theprovision of at least the first and second wind farm output.
 2. Methodaccording to claim 1, characterized in that at least the first andsecond wind farm each comprise a wind farm control unit for controllingthe respective wind farm, the central control unit is connected to thesewind farm control units and the central control unit controls theprovision of the first and second wind farm output by means of therespective wind farm control unit of at least the first and second windfarm.
 3. Method according to claim 1, characterized in that the centralcontrol unit records status variables for the supply network, values forthe total power output fed in and/or external default values.
 4. Themethod according to claim 1, characterized in that at least the firstand second wind farm feed the power thereof to be fed in for provisioninto an intermediate network, wherein in each case, the intermediatenetwork is connected to the respective wind farm by means of atransformer to step up an electrical voltage in the wind farm to ahigher electrical voltage in the intermediate network and/or theintermediate network is connected to the electrical supply network bymeans of a transformer to step up an electrical voltage in theintermediate network to a higher electrical voltage in the supplynetwork.
 5. Method according to claim 1, characterized in that thecentral control unit controls the feed into the electrical supplynetwork as a function of at least one status variable in the supplynetwork as a function of a grid sensitivity of the supply network withreference to a feed point and/or as a function of a short-circuit ratio.6. Method according to claim 1, characterized in that the centralcontrol unit for the feed into the electrical supply network controlsthe amount of active power to be fed in, the amount of reactive power tobe fed in, and/or the consumption of electrical power in a powerconsumption device, in particular in a loss resistance device.
 7. Themethod according to claim 1, characterized in that the central controlunit records current status variables in the electrical supply network,in particular frequency and voltage amplitude, and, as a functionthereof, controls the provision of at least the first and second windfarm output and/or each wind farm control unit provides informationconcerning at least one status variable for the respective wind farm andthe information contains at least one piece of information from the listcomprising: the currently available power, the power expected to beavailable within a predetermined forecast period and changes expected inthe available power.
 8. The method according to claim 1, characterizedin that the central control unit functions as a phase shifter and/orpower is fed into the grid in such a way that disturbances in the supplynetwork are entirely or partially compensated for.
 9. Wind farmarrangement for feeding electrical power into an electrical supplynetwork comprising: at least a first and a second wind farm in each casecomprising a plurality of wind energy installations, an intermediateelectrical grid that is connected to the wind farms, which intermediatenetwork transmits electrical wind farm output provided by the connectedwind farms and a central control unit for feeding in a total poweroutput that is at least partially generated from the wind farm outputsand for controlling the individual wind farm outputs provided by theconnected wind farms.
 10. (canceled)
 11. The wind farm arrangementaccording to claim 9, characterized in that in each case, theintermediate network is connected to the respective wind farm by meansof a transformer to step up an electrical voltage in the wind farm to ahigher electrical voltage in the intermediate network and/or theintermediate network is connected to the electrical supply network bymeans of a transformer to step up an electrical voltage in theintermediate network to a higher electrical voltage in the supplynetwork.
 12. Wind farm arrangement for feeding electrical power into anelectrical supply network comprising: at least a first and a second windfarm in each case comprising a plurality of wind energy installations,an intermediate electrical grid that is connected to the wind farms,which intermediate network transmits electrical wind farm outputprovided by the connected wind farms, and a central control unit forfeeding in a total power output that is at least partially generatedfrom the wind farm outputs and for controlling the individual wind farmoutputs provided by the connected wind farms, wherein the wind farmarrangement uses a method according to claim 1.